A variable resonator capable of independently changing the resonance frequency and the bandwidth of the resonance frequency is disclosed in Japanese Patent Application Laid-Open No. 2008-206078.
As shown in FIG. 18, the variable resonator comprises an annular line part 1, three or more variable reactance blocks 2 connected to the annular line part 1, and a plurality of switches 3 connected to the annular line part 1. The variable reactance blocks 2 are connected to the annular line part 1 at regular intervals along the circumference thereof, and the switches 3 are connected to the annular line part 1 at different positions.
The resonance frequency can be changed by changing the reactance value of the variable reactance blocks 2, and the bandwidth can be changed by changing the switch 3 to be turned on.